Inverted magnetron having adjacent anode cavities coupled in opposite phase to a central stabilizing cavity



1965 E. T. DOWNING ETAL INVERTED MAGNETRON HAVING ADJACENT ANODECAVITIES COUPLED IN OPPOSITE PHASE TO A CENTRAL STABILIZING CAVITY FiledAug. 5, 1964 F/GTJ //VVE/VTOR$ EDWARD I DUW/Vl/VG W/LL/AM A. HOWE-RSAGE/VT folz United States Patent 3,289,036 INVERTED MAGNETRON HAVINGADJACENT ANODE CAVITIES COUPLED IN OPPOSITE PHASE TO A CENTRALSTABILIZING CAVITY Edward T. Downing, Winchester, and William A. Bowers,Berlin, Mass., assignors to Raytheon Company, Lexington, Mass., acorporation of Delaware Filed Aug. 5, 1964, Ser. No. 387,572 9 Claims.(Cl. 315-3953) This invention relates to crossed-field electrondischarge devices and, more particularly, to a magnetron device whereinthe amode'system is within a coaxial cathode.

In order to satisfy requirements for magnetron tubes of greater powerhandling capability and higher frequency range, attempts have been madeto construct so called inverted magnetron devices wherein the anodesystem is arranged within a coaxial cathode in contrast to the moreconventional arrangement in which the cathode is within a coaxial anode.Reference is had to the text Crossed- Field Microwave Devices, vol. II,by E. O. Kress, Academic Press 1961, chapters 3.1 and 5.5, for adisscusion of such attempts. One of the obvious advantages to such acoaxial cathode structure is the increase of cathode emission surfacearea. The effective anode area presented to the cathode is alsoincreased, since the anode segments or vanes are located outside,instead of inside, the resonant cavity structure at a greater distancefrom the axis of the device which permits a greater number of vanes tobe employed. However, as noted in the referenced text, inversion of themagnetron with its complicated electron interaction is not as simple intheory as inversion of a tube with simpler electron trajectories, suchas a tetrode or triode. Some of the difficulties associated with suchinversion is that mode separation is decreased to the extent that thetube does not socillate in a stable fashion and that circuit efliciencyis decreased so that the tube does not oscillate at all.

Accordingly, it is an object of the present invention to provide amagnetron device having high power handling capabilities at highfrequencies with improved mode stability and operating efiiciency.

To this end, there is provided in accordance with the invention anelectrode structure comprising a centrally located cylindricalstabilizing cavity of length substan tially equal to an integral numberof wavelengths of the mid-band of the operating frequency, an anodestructure having vanes extending radially outward from the periphery ofthe cavity, said anode vanes forming anode cavities therebetween,adjacent anode cavities being coupled to opposite ends of saidstabilizing cavity to obtain symmetrical coupling, and a cylindricalemitting cathode facing toward the vanes. The device of the inventionmay be best described as an integral cavity magnetron since, unlike mostmagnetrons, every anode cavity is coupled to the stabilizing cavity. TheRF. energy distribution in each anode cavity thus becomes equal becauseeach anode cavity is coupled to one of two equal stabilizing cavityelectromagnetic fields. Two electric and two magnetic fields with eachspecific field 180 out of phase with its adjacent field, exist in thestabilizing cavity because the stabilizing cavity, as aforesaid, is afull wavelength long. However, it should be noted that it is within thecontemplation of the invention that the cavity length L can be made anyintegral number of /2 wavelength long so as to satisfy the relationshipL=n)\/2 where n is an integer greater than or equal to 2. Thestabilizing cavity is, in essence, symmetrically integrated to the wavestructure and hence the term integral cavity.

Accordingly, it will be seen from the description to follow that theintegral cavity magnetron of the in- 3,289,036 Patented Nov. 29, 1966ice vention provides: very large anode and cathode surfaces because ofthe inside-out construction coupled with the one wavelength cavitystructure, thus resulting in the generation of higher power at higherfrequencies, as well stabilized anode cavity structure of a size andconstruction compatible with the use of a large number of vanes andaccompanying large anode area, and symmetrical coupling by virtue of thefull wavelength cavity and integral coupling arrangement, resulting inimproved mode stability and operating efficiency.

Other objects, features and advantages of the invention will becomeapparent from the following description taken in connection with theaccompanying drawings in which:

FIG. 1 is a cross section of the integral cavity magnetron structure ofthe invention;

FIG. 2 is an enlarged perspective view of pertinent portions of theintegral cavity magnetron structure of the invention shown in FIG. 1;and

FIG. 3 is a graph plotting the quality factor Q versus the ratio ofdiameter to length for various cavities.

In FIGS. 1 and 2. there is shown a magnetron structure 10 comprising ahollow anode cylinder 14, forming a cavity 12, and which may be of anydesired conductive material, such as copper. Extending radially outwardfrom cylinder 14 are a plurality of anode elements 16, which, in thisembodiment though not by way of limitation, comprises substantiallyrectangular plates with surfaces parallel to the longitudinal axis 15 ofcylinder 14. One end of cavity 12 is sealed off from the atmosphere by amicrowave window 24 which is transparent to electromagnetic energy andcomprised of suitable dielectric material. The remaining end of cavity12 is sealed by solid support piece 21 of cylinder 14. In cavity 12 andsuspended from microwave window 24 is a coupling iris 19 located adistance nh/Z from surface 40 of cavity 12. It should be noted that Xrepresents the wavelength of the mid-band of the frequency of the energypropagated in the cavity, and n is an integer greater than or equal to2. It is further noted that iris 19 instead of being suspended fromwindow 24 could alternatively be supported by a thin rod extending fromsurface 40 if desired. Iris 19 is formed of metal such as copper andpartially closes one end of cavity 12 while permitting a predeterminedportion of the energy propagated in the cavity to egress throughmicrowave window 24. It is further noted that output ports could beprovided at either or both ends of cavity 12 as desired and theinvention is not to be limited to the particular manner of extractingenergy shown herein.

Concentric with and encircling the window end of cylinder 14 is amagnetic pole piece 13 which has its central opening extending axiallytherein concentric with waveguide 11 to enable R.F. energy from themagnetron structure to be coupled out through window 24 to a utilizationdevice, not shown. A second magnetic pole piece 23 is provided inconcentric encirclement of support piece "21. Concentric insulativediscs 30' and 31 are provided intermediate the pole pieces and thesupport piece 21 and waveguide 11 to vacuum seal the ends of themagnetron interaction space 17. A cathode cylinder or ring 22 coatedwith electron emissive material is provided encircling the axis of innercylinder 14 and coaxial to the anode vanes 16. Cathode 22 is supportedby insulative member 41 disposed intermediate pole pieces 13 and 23.

The integral cavity magnetron of FIGS. 1 and 2 thus obtained may belooked upon descriptively as formed from two inverted coaxial magnetronsplaced end-to-end so that their axes coincide in a common axis 15.

The stabilizing cavity thus formed is a full wavelength cavitycontaining two electric fields illustrated by dotted 3 lines 32 and 33and two magnetic fields illustrated by solid lines 34 and 35 with eachfield 180 out of phase with its adjacent field. Since the stabilizingcavity is a full wavelength cavity, two fields of opposite polarityexist therein. The fields in one-half of the stabilizing cavity 12 areconnected to alternate vane resonators or interaction spaces formed bythe vanes and cathode structure by means of coupling slots 18. Thefields in coupled alternate resonators are phased by the cavity; hencealternate resonators which are all fed from the same half of the cavitywill all be in phase. The remaining resonators which are fed from theremaining half of the cavity by means of slots disposed into the remaining half of the cavity will be of opposite phase polarity. Therefore, inthe integral cavity magnetron, unlike the prior art structures, everyvane or anode resonator is coupled to the stabilizing cavity. The R.-F.energy distribution in each resonator is equal because each resonator iscoupled to one of the two stabilizing cavity fields and these cavityfields are intimately coupled together. The stabilizing cavity is, inessence, symmetrically integrated to the vane structure; therefore, thedevice is called an integral cavity magnetron. Such intimate andsymmetrical coupling between the vane structure and stabilizing cavityresults in a tube with less tendency towards moding and with betterstarting characteristics.

Furthermore, the integral cavity feature results in an overall increasein efficiency resulting from the higher unloaded Q of the stabilizingcavity. This feature of the invention may best be appreciated from ananalysis of FIG. 3 which is a plot of the ratio of the cavity diameter Dto cavity length L versus the normalized Q of a full wavelength cavity(curve a) operating in the TE mode and a half wavelength cavity (curve12) operated in the TE mode. It may be seen that in both curves a and bthe optimum Q occurs when the ratio of D/ L is unity. At that point inthe curve the Q of the full wavelength cavity is about 20% higher thanthe Q of the half Wavelength cavity. A higher unloaded Q will provideimproved circuit efliciency; hence, the circuit efficiencies will behigher in the full wavelength integral cavity of the invention for agiven loaded Q.

Although there have been described what have been considered to bepreferred embodiments of the present invention, various modificationsand adaptations thereof will be apparent to those skilled in the art.For example, the integral cavity magnetron may be-employed to obtainconsiderable amplification of an input signal since the stabilizingcavity geometry is such that it may or may not be constructed asreentrant, depending on the application desired. To obtain amplificationan input cavity is isolated from an output cavity or cavities by meansof a metallic wall perpendicular to the axis of the output cavities andfilling the cross-sectional area bounded by the cylindrical cavity wall.The coupling slots in the input cavity couple input energy onto the vanestructure where amplification is obtained by magnetron type interaction.The output cavity or cavities couple the RF. energy to the output anddefine the pass band of the system. A plurality of cavities may beemployed, stagger-tuned to increase the pass band and the gain. In thisinstance over-all gain may be defined in terms of the anode length whichwill ultimately be dependent upon the number of cavities employed.Accordingly, it is desired that the invention not be limited except asset forth in the appended claims. I

What is claimed is:

1. An electrode structure comprising:

an anode cylinder having inner and outer longitudinal surfaces anddefining an integral stabilizing cavity;

a cathode cylinder encircling said anode cylinder;

a plurality of anode vanes attached to an outer surface of said anodecylinder and forming resonant anode cavities between said vanes;

a first plurality of slots extending through said anode cylinder andcoupling alternate anode cavities to the upper portion of saidstabilizing cavity;

and a second plurality of slots extending through said anode cylinderand coupling the remaining anode cavities to the lower portion of saidstabilizing cavy;

adjacent slots of said first and second pluralities being spaced apartaxially of the anode cylinder.

2. The apparatus of claim 1 wherein the electrical length of the anodecylinder is substantially equal to ilk/2 wherein n is an integer greaterthan or equal to 2 and A is the wavelength of the midband of theoperating frequency.

3. In a crossed field device:

an anode cylinder having inner and outer longitudinal surfaces anddefining an integral stabilizing cavity;

a cathode cylinder coaxial to and encircling said anode cylinder;

a plurality of anode vanes attached to an outer surface of said anodecyhnder and forming resonant anode cavities between said vanes;

a first plurality of slots extending through the inner surface to theouter surface of said anode cylinder coupling every other anode cavityto the upper portion of said stabilizing cavity;

a'second plurality of slots extending through the inner surface to theouter surface of said anode cylinder coupling the remaining anodecavities to the lower portion of said stabilizing cavity;

and means at at least one end of said anode cylinder forfcoupling energyfrom the stabilizing cavity to a load device.

4. An inverted magnetron having a cathode electrode coaxial to andencircling a vaned anode cylinder forming a plurality of resonant anodecavities between the vanes in which means are provided for couplingalternate anode vane cavities to the upper half of an interiorcylindrical cavity formed by said anode cylinder and for couplingremaining anode vane cavities to the lower half of said cylindricalcavity whereby every anode vane cavity is coupled alternately to theupper and lower portions of said cavity.

5. The apparatus of claim 4- wherein the coupling means comprises afirst plurality of slots located adjacent each other along thecircumference of said cylindrical cavity and a second plurality of slotsspaced apart axially from said firs-t plurality of slots. 6. Theapparatus of claim 4 in which the efiective length of the interior ofsaid cylindrical cavity is equal to nA/Z wherein n is an integer greaterthan or equal to 2 and A is the wavelength of the midband of theoperating frequency of said magnetron.

7. An electrode structure comprising:

a hollow cylindrical anode structure forming a stabilizing cavity in theinterior thereof, said anode structure having vanes extending radiallyoutward from the periphery of said structure forming anode cavitiestherebetween, adjacent anode cavities being coupled to opposite ends ofsaid stabilizing cavity for symmetrically coupling energy therebetween,said stabilizing cavity of length substantially equal to an integralnumber of wavelengths of the midband of the operating frequency; A

and a cylindrical emitting cathode coaxial to and encircling said vanes.

- 8. An electrode structure comprising:

a hollow cylindrical anode structure forming a stabilizing cavity in theinterior thereof, said anode structure having vanes extending radiallyoutward from the periphery of said structure forming anode cavitiestherebetween, adjacent anode cavities being coupled to opposite ends ofsaid stabilizing cavity for ymmetrically coupling energy therebetween,said 3,289,086 5 6 stabilizing cavity of length substantially equal toan References Cited by the Examiner integral number of Wavelengths ofthe midband of UNITED STATES PATENTS the operating frequency;

1i 0 th d t d 2,815,469 12/1957 Sixsrnit-h 31539.77 1; 12:21P Ca 0 ecoaxial 0 an enclrchng 5 3,096,462 7/1963 Feinstein 315-4915 and meansdisposed at, at least, one end of said sta- References Cited by theApplicant bilizing cavity for extracting predetermined portions UNITEDSTATES PATENTS of the energy in said cavity therefrom. 9. The apparatusof claim '8 wherein the means for extracting energy from the stabilizingcavity comprises 10 HERMAN KARL SAALBACH Primary Examiner an irisdependent from a microwave Window sealing off an end of said Stabilizingcavity P. L. GENSLER, Asszstant Examiner.

2,419,172 4/1947 Smith.

1. AN ELECTRODE STRUCTURE COMPRISING: AN ANODE CYLINDER HAVING INNER ANDOUTER LONGITUDINAL SURFACES AND DEFINING AN INTEGRAL STABILIZING CAVITY;A CATHODE CYLINDER ENCIRCLING SAID ANODE CYLINDER; A PLURALITY OF ANODEVANES ATTACHED TO AN OUTER SURFACE OF SAID ANODE CYLINDER AND FORMINGRESONANT ANODE CAVITIES BETWEEN SAID VANES; A FIRST PLURALITY OF SLOTSEXTENDING THROUGH SAID ANODE CYLINDER AND COUPLING ALTERNATE ANODECAVITIES TO THE UPPER PORTION OF SAID STABILIZING CAVITY; AND A SECONDPLURALITY OF SLOTS EXTENDING THROUGH SAID ANODE CYLINDER AND COUPLINGTHE REMAINING ANODE CAVITIES TO THE LOWER PORTION OF SAID STABILIZINGCAVITY; ADJACENT SLOTS OF SAID FIRST AND SECOND PLURALITES BEING SPACEDAPART AXIALLY OF THE ANODE CYLINDER.